1. Field of the Invention
The invention relates to an improved pump assembly for a hydraulic vehicle brake system.
2. Description of the Prior Art
One pump assembly of this type with which this invention is concerned is known from German Patent Disclosure DE 196 32 167 A1. The known pump assembly has an electric motor as well as a piston pump that is drivable with the electric motor. The piston pump has an eccentric sleeve, which by means of a torque-transmitting sleeve is connected in a manner fixed against relative rotation to a motor shaft of the electric motor. The torque-transmitting sleeve forms a rotationally rigid, non-shiftable coupling, which compensates for radial and angular errors of alignment as well as axial displacements between the eccentric sleeve and the motor shaft. By rotational drive of the eccentric sleeve, pump pistons that are disposed radially to the eccentric sleeve in a pump housing are driven to execute a reciprocating stroke motion, by which fluid (brake fluid) is pumped in a manner known per se.
The torque-transmitting sleeve decouples the motor shaft from radial stresses that the pump pistons exert on the eccentric sleeve; no bending stress is transmitted to the motor shaft. The eccentric sleeve is rotatably supported by a bearing, hereinafter called a pump bearing, that is disposed in the eccentric sleeve and on a pump shaft that is mounted solidly in the pump housing and protrudes into the eccentric sleeve. The pump bearing braces the eccentric sleeve against radial stresses that the pump pistons exert on the eccentric sleeve. The pump bearing of the known pump assembly is located in a radial plane with the pump pistons disposed radially to the eccentric sleeve. Since no bending stress is transmitted to the motor shaft, the radial stresses must be intercepted solely by the pump shaft, which is braced on only one side in the pump housing. Accordingly, the pump shaft experiences major bending stress and force distribution is unfavorable.
In the pump assembly of the invention, the eccentric sleeve is rigidly pressed onto the motor shaft and in this way rigidly joined to the motor shaft. A motor bearing near the pump and the pump bearing, that is, the two bearings that brace the eccentric sleeve against the radial stresses of the pump pistons, are furthermore disposed on both sides of an engagement point of the pump pistons on the eccentric sleeve. Radial stresses exerted on the eccentric sleeve by the pump pistons are thereby distributed to the pump bearing and the motor bearing near the pump; the bearing load on the individual bearing is thus reduced. The bearings can accordingly be made smaller, which economizes on installation space. Another advantage of the invention is that the pump shaft, which is mounted in the pump housing and on which the eccentric sleeve is rotatably supported, is not subjected to bending stress by the pump pistons, since the eccentric sleeve is radially braced via the motor bearing near the pump. Pressing the eccentric sleeve onto the motor shaft produces a favorable distribution and transmission of force and moment within the motor shaft and the eccentric sleeve. The component formed of the motor shaft with the eccentric sleeve pressed onto it can be considered, in terms of force and moment distribution, as a one-piece component.
The pump bearing of the invention makes it possible to use a stepless motor shaft which can thus be produced economically. Another advantage of the invention is that the motor shaft and the eccentric sleeve can be produced with high precision and low tolerance, which makes a small bearing plate possible, which in turn reduces noise.
According to one embodiment, the motor bearing near the pump is mounted in a motor housing of the electric motor. This includes the possibility that a motor bearing near the pump protrudes axially into the pump housing in the manner of a peg connection, and thereby centers the electric motor on the piston pump when the electric motor and the piston pump are put together. Mounting the motor bearing near the pump in the motor housing of the electric motor has the advantage that the electric motor can be tested separately from the piston pump.
In one feature of the invention, it is provided that the motor bearing near the pump be used as a so-called fixed bearing, which takes on the task of axially guiding the motor shaft and eccentric sleeve pressed onto it. To that end, claim 4 provides for the use of a ball bearing for the motor bearing near the pump, the inner and outer ring of the ball bearing being axially fixed.
The two other bearings, namely the pump bearing and the eccentric bearing, are provided in the form of so-called loose bearings, which do not axially guide the motor shaft. For the sake of a small structural size, these two bearings may be embodied as needle bearings.
The pump assembly of the invention is intended in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS (for anti-lock brake system), TCS (traction control system), VDC (vehicle dynamics control) and EHB (electrohydraulic brake system) are used for such brake systems. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to pump brake fluid out of a supply container into a wheel brake cylinder or a plurality of wheel brake cylinders (TCS or VDC or EHB). In a brake system with wheel slip control (ABS or TCS) and/or a brake system serving as a steering aid (VDC) and/or an electrohydraulic brake system (EHB), the pump is needed. With the wheel slip control (ABS or TCS), locking of the wheels of the vehicle during a braking event involving strong pressure on the brake pedal (ABS) and/or spinning of the driven wheels of the vehicle in the event of strong pressure on the gas pedal (TCS) can for instance be prevented. In a brake system serving as a steering aid (VDC), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB), in which the pump pumps the brake fluid into the wheel brake cylinder or wheel brake cylinders if an electric brake pedal sensor detects an actuation of the brake pedal, or in which the pump is used to fill a reservoir of the brake system.